High stability polymer compositions with poly(alkyl)acrylate compounds for enhanced oil recovery applications

ABSTRACT

Liquid polymer and inverse emulsion compositions comprising: one or more hydrophobic liquids having a boiling point at least about 100° C.; one or more acrylamide-(co)polymers; one or more emulsifier surfactants; one or more inverting surfactants; and one or more poly(alkyl)acrylate compounds. When the composition is inverted in an aqueous solution, it provides an inverted solution having a filter ratio using a 1.2 micron filter (FR1.2) of about 1.5 or less.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.62/527,675, filed Jun. 30, 2017.

FIELD OF THE INVENTION

The present disclosure relates to polymer compositions comprising(co)polymers and poly(alkyl)acrylate compounds, which provide increasedstability without detrimentally impacting the filter ratio.

BACKGROUND

Polymer flooding is a technique used in enhanced oil recovery (EOR). Itinvolves injecting an aqueous solution of a water-soluble thickeningpolymer (e.g., high molecular weight polyacrylamide) into a mineral oildeposit. As a result, it is possible to mobilize additional mineral oilin the formation. Details of polymer flooding and of polymers suitablefor this purpose are disclosed, for example, in “Petroleum, Enhanced OilRecovery,” Kirk-Othmer, Encyclopedia of Chemical Technology, onlineedition, John Wiley and Sons, 2010.

The aqueous polymer solution used in polymer flooding typically has anactive polymer concentration of from about 0.05 weight percent to about0.5 weight percent. Additional components may be added to the aqueouspolymer solution, such as surfactants or biocides.

Large volumes of the aqueous polymer solution are necessary for polymerflooding and the process may go on for months or even years. Given thevolumes required, conventional polymer flooding involves dissolving thepolymer (in the form of a dry powder) on site using fresh water, brine,sea water, production water, and/or formation waste. Unfortunately, theconventional dissolution process is time-consuming and there are fewways to decrease the time without damaging the polymer. The spacerequired for on-site dissolution of dry powder polymers is alsosignificant. While space is normally not a limiting factor in land-basedoil production, space is limited in off-shore oil production. Whetherland-based or off-shore, the necessary equipment for conventional, drypowder-based on site preparation of polymer flooding solutions isexpensive.

Inverse emulsions (water-in-oil) and liquid polymers offer analternative to on-site dissolution of dry powders, particularly foroff-shore oil production. The active polymer concentration in inverseemulsions is typically about 30 weight percent, and is higher in liquidpolymer composition. For use, the inverse emulsion or liquid polymercomposition is diluted with water to provide the desired finalconcentration of the polymer.

The description herein of certain advantages and disadvantages of knownmethods and devices is not intended to limit the scope of the presentinvention. Indeed, the present embodiments may include some or all ofthe features described above without suffering from the samedisadvantages.

SUMMARY

In view of the foregoing, one or more embodiments include: a liquidpolymer or inverse emulsion composition comprising: one or morehydrophobic liquids having a boiling point at least about 100° C.; oneor more acrylamide-(co)polymers; one or more emulsifier surfactants; oneor more inverting surfactants; and one or more poly(alkyl)acrylatecompounds; wherein, when the composition is inverted in an aqueoussolution, it provides an inverted polymer solution having a filter ratiousing a 1.2 micron filter (FR1.2) of about 1.5 or less.

Also provided herein are methods for hydrocarbon recovery. The methodsfor hydrocarbon recovery can comprise providing a subsurface reservoircontaining hydrocarbons there within; providing a wellbore in fluidcommunication with the subsurface reservoir; preparing an invertedpolymer solution from the liquid polymer or inverse emulsioncompositions described herein; and injecting the inverted polymersolution through the wellbore into the subsurface reservoir.

DETAILED DESCRIPTION

Generally, the various embodiments described herein provide a liquidpolymer or inverse emulsion composition with enhanced stability.

It has been observed that inverse emulsion and liquid polymercompositions typically used for EOR applications tend to form gels andexperience separation of their oil and water phases over time. Inparticular, the shelf-life stability of such compositions having highpolymer actives may decrease as the solids content is raised. In someinstances, such compositions may deteriorate to form an oil film and ahard cake in packaging within the amount of time it takes to manufactureand transport the compositions to the platform (e.g., about 30 days).The hard cake may not be readily redistributed in the composition, whichresults in lower overall polymer actives in the deterioratedcomposition. Thickening additives may be used to minimize settling ofthe inverse emulsion and liquid polymer compositions, however they mayhave a detrimental effect on the filter ratio of the compositions.

In particular, the compositions described herein provide increasedstability without detrimentally impacting the filter ratio. Thecompositions comprise one or more stabilizing agents, orpoly(alkyl)acrylate compounds, which may prevent or minimizesedimentation and/or caking of solids in the liquid polymer or inverseemulsion compositions. In embodiments, the compositions comprise anacrylamide (co)polymer and one or more poly(alkyl)acrylate compounds. Incertain embodiments, the compositions are formed by adding one or morepoly(alkyl)acrylate compounds to a liquid polymer or inverse emulsioncomposition comprising one or more acrylamide-(co)polymers, one or morehydrophobic liquids, one or more emulsifier surfactants, and one or moreinverting surfactants. The various embodiments described herein alsoprovide inverted polymer solutions derived from the compositions andmethods for preparing the compositions. The liquid polymer and inverseemulsion compositions can be used in EOR applications.

In EOR applications, the inversion of a conventional liquid polymer orinverse emulsion composition is generally difficult. The requirements ofthe end-users are often very strict: total dissolution in less than 5minutes, completely and continuously. In certain embodiments, a liquidpolymer or inverse emulsion composition dissolves in an aqueous solutionto a final concentration of about 50 to about 15,000 ppm, or about 500to about 5000 ppm in less than about 30 minutes, or less than about 20minutes, or less than about 10 minutes, or less than about 5 minutes.

An inverted polymer solution prepared from the liquid polymer or inverseemulsion compositions provides excellent performance. An invertedpolymer solution according to the embodiments flows through a formationwithout plugging the pores of the formation. Plugging the formation canslow or inhibit oil production. This is especially concerning whereformation permeability is low to start with.

Definitions

As used herein, “enhanced oil recovery” (abbreviated “EOR”) refers tovarious techniques for increasing the amount of crude oil that can beextracted from an oil field that conventional techniques do not recover.

As used herein, “filter ratio” (abbreviated “FR”) or “filter quotient”are used interchangeably herein to refer to a test used to determineperformance of the liquid polymer composition (or the inverted polymersolution derived therefrom) in conditions of low formation permeabilityconsisting of measuring the time taken by given volumes/concentrationsof solution to flow through a filter. The FR generally compares thefilterability of the polymer solution for two equivalent consecutivevolumes, which indicates the tendency of the solution to plug thefilter. Lower FRs indicate better performance.

Two filter ratio test methods are referenced herein. The first method,referred to as “FR5” or “filter ratio using a 5 micron filter,” involvespassing a 500 mL sample of a polymer solution through a 47 mm diameterpolycarbonate filter having 5 micron pores, under 1 bar pressure(+/−10%) of N₂ or argon at ambient temperature (e.g., 25° C.). The timesrequired to obtain 100 g, 200 g, 400 g, and 500 g of filtrate arerecorded, and the FR5 filter ratio is calculated as

$\frac{{{time}\mspace{14mu} {at}\mspace{14mu} 500\mspace{14mu} g} - {{time}\mspace{14mu} {at}\mspace{14mu} 400\mspace{14mu} g}}{{{time}\mspace{14mu} {at}\mspace{14mu} 200\mspace{14mu} g} - {{tim}\; e\mspace{14mu} {at}\mspace{14mu} {100}\mspace{14mu} g}}.$

The second method, referred to as “FR1.2” or “filter ratio using a 1.2micron filter,” involves passing a 200 mL sample of a polymer solutionthrough a 47 mm diameter polycarbonate filter having 1.2 micron pores,under 1 bar pressure (+/−10%) of N₂ or argon at ambient temperature(e.g., 25° C.). The times required to obtain 60 g, 80 g, 180 g, and 200g of filtrate are recorded, and the FR1.2 filter ratio is calculated as

$\frac{{{time}\mspace{14mu} {at}\mspace{14mu} 200\mspace{14mu} g} - {{time}\mspace{14mu} {at}\mspace{14mu} 180\mspace{14mu} g}}{{{time}\mspace{14mu} {at}\mspace{14mu} 80\mspace{14mu} g} - {{time}\mspace{14mu} {at}\mspace{14mu} 60\mspace{14mu} g}}.$

Other filter ratio test methods are known and are used in this field.For example, the filter media used may have a different size (e.g., 90mm), a different pore size, and/or a different substrate (e.g.,nitrocellulose), the pressure may be different (e.g., 2 bars), thefiltering intervals/amounts may be different, and other changes areenvisioned. For example, U.S. Pat. No. 8,383,560 (incorporated herein byreference) describes an FR test method that compares the time taken bygiven volumes of a solution containing 1000 ppm of active polymer toflow through a 5 micron filter having a diameter of 47 mm at a pressureof 2 bars. In comparison, the methods described herein provide a betterscreening method for commercial conditions. In particular, the FR1.2test method described herein, which uses a smaller pore size under lowerpressure, provides more predictable results in commercial field testing.Polymers that provide acceptable results in the FR1.2 test method haveexhibited easier processing with lower risk of formation damage.

As used herein, “inverted” means that the liquid polymer or inverseemulsion composition is dissolved in an aqueous solution, so that thedispersed polymer phase of the liquid polymer or inverse emulsioncomposition becomes a substantially continuous phase, and thehydrophobic liquid phase becomes a dispersed, discontinuous phase. Theinversion point can be characterized as the point at which the viscosityof the inverted polymer solution has substantially reached its maximumunder a given set of conditions. In practice, this may be determined forexample by measuring viscosity of the composition periodically over timeand when three consecutive measurements are within the standard of errorfor the measurement, then the solution is considered inverted.

As used herein, the terms “polymer,” “polymers,” “polymeric,” andsimilar terms are used in their ordinary sense as understood by oneskilled in the art, and thus may be used herein to refer to or describea large molecule (or group of such molecules) that contains recurringunits. Polymers may be formed in various ways, including by polymerizingmonomers and/or by chemically modifying one or more recurring units of aprecursor polymer. A polymer may be a “homopolymer” comprisingsubstantially identical recurring units formed by, e.g., polymerizing aparticular monomer. A polymer may also be a “copolymer” comprising twoor more different recurring units formed by, e.g., copolymerizing two ormore different monomers, and/or by chemically modifying one or morerecurring units of a precursor polymer. The term “terpolymer” may beused herein to refer to polymers containing three or more differentrecurring units. The term “polymer” as used herein is intended toinclude both the acid form of the polymer as well as its various salts.

As used herein, “polymer flooding” refers to an enhanced oil recoverytechnique using water viscosified with soluble polymers. Polymerflooding can yield a significant increase in oil recovery compared toconventional water flooding techniques. Viscosity is increased until themobility of the injectant is less than that of the oil phase in place,so the mobility ratio is less than unity. This condition maximizesoil-recovery sweep efficiency, creating a smooth flood front withoutviscous fingering. Polymer flooding is also applied to heterogeneousreservoirs; the viscous injectant flows along high-permeability layers,decreasing the flow rates within them and enhancing sweep of zones withlower permeabilities. The two polymers that are used most frequently inpolymer flooding are partially hydrolyzed polyacrylamide and xanthan. Atypical polymer flood project involves mixing and injecting polymer overan extended period of time until at least about half of the reservoirpore volume has been injected.

Liquid Polymer Compositions

According to the embodiments, the liquid polymer composition comprisesone or more polymers dispersed in one or more hydrophobic liquids, andone or more poly(alkyl)acrylate compounds. In embodiments, the liquidpolymer composition further comprises one or more emulsifyingsurfactants and one or more inverting surfactants. In embodiments, theliquid polymer composition further comprises a small amount of water,for example less than about 12%, about 10%, about 5%, about 3%, about2.5%, about 2%, or about 1% by weight water, based on the total amountof all components of the liquid polymer composition. In embodiments, theliquid polymer composition can be water-free or at least substantiallywater-free. The liquid polymer composition may include one or moreadditional components, which do not substantially diminish the desiredperformance or activity of the composition. It will be understood by aperson having ordinary skill in the art how to appropriately formulatethe liquid polymer composition to provide necessary or desired featuresor properties.

In embodiments, a liquid polymer composition comprises: one or morehydrophobic liquids having a boiling point at least about 100° C.; atleast about 39% by weight of one or more acrylamide-(co)polymers; one ormore emulsifier surfactants; one or more inverting surfactants; and oneor more poly(alkyl)acrylate compounds; wherein, when the composition isinverted in an aqueous solution, it provides an inverted polymersolution having a filter ratio using a 1.2 micron filter (FR1.2) ofabout 1.5 or less. In embodiments, the liquid polymer composition mayoptionally comprise one or more additional stabilizing agents.

In embodiments, when the liquid polymer composition is inverted in anaqueous solution, providing an inverted polymer solution having about 50to about 15,000 ppm, about 500 to about 5000 ppm, or about 500 to about3000 ppm, active polymer concentration, the inverted polymer solutionhas a viscosity of at least about 10 cP, or at least about 20 cP, atabout 40° C., and a FR1.2 (1.2 micron filter) of about 1.5 or less.

In embodiments, when the liquid polymer composition is inverted in anaqueous solution, providing an inverted polymer solution having about 50to about 15,000 ppm, about 500 to about 5000 ppm, or about 500 to about3000 ppm, active polymer concentration, the inverted polymer solutionhas a viscosity of at least about 10 cP, or at least about 20 cP, atabout 30° C., and a FR1.2 (1.2 micron filter) of about 1.5 or less.

In embodiments, when the liquid polymer composition is inverted in anaqueous solution, providing an inverted polymer solution having about 50to about 15,000 ppm, about 500 to about 5000 ppm, or about 500 to about3000 ppm, active polymer concentration, the inverted polymer solutionhas a viscosity of at least about 10 cP, or at least about 20 cP, atabout 25° C., and a FR1.2 (1.2 micron filter) of about 1.5 or less.

In embodiments, when the liquid polymer composition is inverted in anaqueous solution, providing an inverted polymer solution having about 50to about 15,000 ppm, about 500 to about 5000 ppm, or about 500 to about3000 ppm, active polymer concentration, the inverted polymer solutionhas a viscosity of at least about 10 cP, or at least about 20 cP, atabout 40° C., and a FR1.2 (1.2 micron filter) of about 1.1 to about 1.3.

In embodiments, when the liquid polymer composition is inverted in anaqueous solution, providing an inverted polymer solution having about 50to about 15,000 ppm, about 500 to about 5000 ppm, or about 500 to about3000 ppm, active polymer concentration, the inverted polymer solutionhas a viscosity of at least about 10 cP, or at least about 20 cP, atabout 30° C., and a FR1.2 (1.2 micron filter) of about 1.1 to about 1.3.

In embodiments, when the liquid polymer composition is inverted in anaqueous solution, providing an inverted polymer solution having about 50to about 15,000 ppm, about 500 to about 5000 ppm, or about 500 to about3000 ppm, active polymer concentration, the inverted polymer solutionhas a viscosity of at least about 10 cP, or at least about 20 cP, atabout 25° C., and a FR1.2 (1.2 micron filter) of about 1.1 to about 1.3.

In embodiments, when the liquid polymer composition is inverted in anaqueous solution, providing an inverted polymer solution having about 50to about 15,000 ppm, about 500 to about 5000 ppm, or about 500 to about3000 ppm, active polymer concentration, the inverted polymer solutionhas a viscosity of at least about 10 cP, or at least about 20 cP, atabout 40° C., and a FR1.2 (1.2 micron filter) of about 1.2 or less.

In embodiments, when the liquid polymer composition is inverted in anaqueous solution, providing an inverted polymer solution having about 50to about 15,000 ppm, about 500 to about 5000 ppm, or about 500 to about3000 ppm, active polymer concentration, the inverted polymer solutionhas a viscosity of at least about 10 cP, or at least about 20 cP, atabout 30° C., and a FR1.2 (1.2 micron filter) of about 1.2 or less.

In embodiments, when the liquid polymer composition is inverted in anaqueous solution, providing an inverted polymer solution having about 50to about 15,000 ppm, about 500 to about 5000 ppm, or about 500 to about3000 ppm, active polymer concentration, the inverted polymer solutionhas a viscosity of at least about 10 cP, or at least about 20 cP, atabout 25° C., and a FR1.2 (1.2 micron filter) of about 1.2 or less.

In embodiments, the liquid polymer composition, prior to inversion,comprises less than about 12% water by weight, less than about 10% byweight, less than about 7% water by weight, less than about 5% water byweight, or less than about 3% water by weight. In embodiments, theliquid polymer composition, prior to inversion comprises from about 1 toabout 12% water by weight, or about 1% to about 5% water by weight basedon the total amount of all components of the composition.

In embodiments, the liquid polymer composition, prior to inversion,comprises at least about 39%, about 40%, about 45%, about 50%, about55%, about 60%, about 65%, about 70%, or about 75% polymer by weightbased on the total amount of all components of the composition.

In embodiments, the water in the liquid polymer composition may befreshwater, saltwater, or a combination thereof. Generally, the waterused may be from any source, provided that it does not contain an excessof compounds that may adversely affect other components in thecomposition.

In embodiments, the inverted polymer solution has a viscosity greaterthan about 10 cP at about 25° C. In embodiments, the inverted polymersolution has a viscosity in the range of about 10 cP to about 35 cP,about 15 to about 30, about 20 to about 35, or about 20 to about 30, atabout 25° C. In embodiments, the inverted polymer solution has aviscosity greater than about 10 cP at about 30° C. In embodiments, theinverted polymer solution has a viscosity in the range of about 10 cP toabout 30 cP, about 15 cP to about 30 cP, about 15 cP to about 25 cP,about 25 cP to about 30 cP, about 15 cP to about 22 cP, about 20 cP toabout 30 cP, at about 30° C. In embodiments, the inverted polymersolution has a viscosity greater than about 10 cP at about 40° C. Inembodiments, the inverted polymer solution has a viscosity in the rangeof about 10 cP to about 35 cP, about 15 cP to about 35 cP, about 15 cPto about 25 cP, about 15 cP to about 22 cP, about 20 cP to about 30 cP,at about 40° C.

In embodiments, the liquid polymer compositions, when inverted in anaqueous solution, provide an inverted polymer solution having a FR1.2 ofabout 1.5 or less. Put another way, an inverted polymer solution that isderived from the liquid polymer composition disclosed herein provides anFR1.2 of about 1.5 or less. In field testing, the compositions (uponinversion) exhibit improved injectivity over commercially-availablepolymer compositions, including other polymer compositions having an FR5(using a 5 micron filter) of about 1.5 or less. In embodiments, theliquid polymer compositions, when inverted in an aqueous solution,provide an inverted polymer solution having a FR1.2 of about 1.1 toabout 1.4, about 1.1 to about 1.35, about 1.0 to about 1.3, or about 1.1to about 1.3.

In embodiments, a liquid polymer composition when inverted has an FR1.2(1.2 micron filter) of about 1.5 or less, about 1.4 or less, about 1.3or less, about 1.2 or less, or about 1.1 or less. In embodiments, theliquid polymer composition that is inverted has an FR5 (5 micron filter)of about 1.5 or less, about 1.4 or less, about 1.3 or less, about 1.2 orless, or about 1.1 or less. In embodiments, the liquid polymercomposition that is inverted has an FR1.2 of about 1.2 or less and a FR5of about 1.2 or less.

In embodiments, the inverted polymer solution has a FR1.2 of about 1.5or less, about 1.4 or less, about 1.3 or less, about 1.2 or less, orabout 1.1 or less. In embodiments, the inverted polymer solution has anFR5 of about 1.5 or less, about 1.4 or less, about 1.3 or less, about1.2 or less, or about 1.1 or less. In other embodiments, the invertedpolymer solution has an FR5 of about 1.5 or less, and an FR1.2 of about1.5 or less.

Inverse Emulsion Compositions

According to the embodiments, an inverse emulsion composition comprisesone or more polymers emulsified in one or more hydrophobic liquids, andone or more poly(alkyl)acrylate compounds. In embodiments, the inverseemulsion composition further comprises one or more emulsifyingsurfactants and one or more inverting surfactants. The inverse emulsioncomposition may include one or more additional components, which do notsubstantially diminish the desired performance or activity of thecomposition. It will be understood by a person having ordinary skill inthe art how to appropriately formulate the inverse emulsion compositionto provide necessary or desired features or properties.

In embodiments, the inverse emulsion composition further compriseswater. In embodiments, the water is in the emulsified polymer phase. Inembodiments, the inverse emulsion comprises greater than about 12% byweight water, based on the total amount of all components of thecomposition. In embodiments, the water in the inverse emulsioncomposition may be freshwater, saltwater, or a combination thereof.Generally, the water used may be from any source, provided that it doesnot contain an excess of compounds that may adversely affect othercomponents in the composition.

In embodiments, the inverse emulsion composition comprises: one or morehydrophobic liquids having a boiling point at least about 100° C.; up toabout 35% by weight of one or more acrylamide-(co)polymers; one or moreemulsifier surfactants; one or more inverting surfactants; and one ormore poly(alkyl)acrylate compounds, when the composition is inverted inan aqueous solution, it provides an inverted polymer solution having afilter ratio using a 1.2 micron filter (FR1.2) of about 1.5 or less. Inembodiments, the inverse emulsion composition may optionally compriseone or more other stabilizing agents.

In embodiments, when the inverse emulsion composition is inverted in anaqueous solution, providing an inverted polymer solution having about500 to about 5000 ppm, or about 500 to about 3000 ppm, active polymerconcentration, the inverted polymer solution has a viscosity of at least20 cP at 40° C., and a FR1.2 (1.2 micron filter) of about 1.5 or less.

In embodiments, when the inverse emulsion composition is inverted in anaqueous solution, providing an inverted polymer solution having about500 to about 5000 ppm, or about 500 to about 3000 ppm, active polymerconcentration, the inverted polymer solution has a viscosity of at least20 cP at 30° C., and a FR1.2 (1.2 micron filter) of about 1.5 or less.

In embodiments, the inverse emulsion composition, prior to inversion,comprises up to about 35% polymer by weight, or up to about 30% polymerby weight, based on the total amount of all components of thecomposition.

In embodiments, the inverted polymer solution has a viscosity in therange of about 25 cP to about 35 cP at about 30° C. In embodiments, theinverted polymer solution has a viscosity greater than about 10 cP atabout 40° C. In embodiments, the inverted polymer solution has aviscosity in the range of about 20 cP to about 30 cP at about 40° C.

In embodiments, the inverse emulsion compositions, when inverted in anaqueous solution, provides an inverted polymer solution having a FR1.2of about 1.5 or less. Put another way, an inverted polymer solution thatis derived from the inverse emulsion composition disclosed hereinprovides an FR1.2 of about 1.5 or less. In field testing, the inverseemulsion compositions, upon inversion, provide improved injectivity overcommercially-available polymer compositions, including other polymercompositions having an FR5 (using a 5 micron filter) of about 1.5 orless.

In embodiments, the inverse emulsion composition, when inverted,provides an inverted polymer solution that has an FR1.2 (1.2 micronfilter) of about 1.5 or less, about 1.4 or less, about 1.3 or less,about 1.2 or less, or about 1.1 or less. In embodiments, the inverseemulsion composition, when inverted, provides an inverted polymersolution that has an FR5 (5 micron filter) of about 1.5 or less, about1.4 or less, about 1.3 or less, about 1.2 or less, or about 1.1 or less.In embodiments, an inverse emulsion composition, when inverted, providesan inverted polymer solution that has an FR1.2 of about 1.2 or less anda FR5 of about 1.2 or less.

In embodiments, the inverted polymer solution of the inverse emulsioncomposition has a FR1.2 of about 1.5 or less, about 1.4 or less, about1.3 or less, about 1.2 or less, or about 1.1 or less. In embodiments,the inverted polymer solution of the inverse emulsion composition has anFR5 of about 1.5 or less, about 1.4 or less, about 1.3 or less, about1.2 or less, or about 1.1 or less. In other embodiments, the invertedpolymer solution of the inverse emulsion composition has an FR5 of about1.5 or less, and an FR1.2 of about 1.5 or less.

Below, the components of the liquid polymer and inverse emulsioncompositions are discussed in greater detail.

Polymer Component

In embodiments, the liquid polymer or inverse emulsion compositioncomprises at least one polymer or copolymer. The at least one polymer orcopolymer may be any suitable polymer or copolymer, such as awater-soluble thickening polymer or copolymer. Non-limiting examplesinclude high molecular weight polyacrylamide, copolymers of acrylamideand further comonomers, for example vinylsulfonic acid or acrylic acid.Polyacrylamide may be partly hydrolyzed polyacrylamide, in which some ofthe acrylamide units have been hydrolyzed to acrylic acid. In addition,it is also possible to use naturally occurring polymers, for examplexanthan or polyglycosylglucan, as described, for example, by U.S. Pat.No. 6,392,596 B1 or CA 832 277.

In embodiments, the liquid polymer or inverse emulsion compositioncomprises one or more acrylamide copolymers. In embodiments, the one ormore acrylamide (co)polymers is a polymer useful for enhanced oilrecovery (EOR) applications. In a particular embodiment, the at leastone polymer is a high molecular weight polyacrylamide or partiallyhydrolyzed products thereof.

In embodiments, the one or more acrylamide (co)polymers are in the formof particles, which are dispersed in the liquid polymer or inverseemulsion composition. In embodiments, the particles of the one or moreacrylamide (co)polymers have an average particle size of about 0.4 μm toabout 5 μm, or about 0.5 μm to about 4 μm, or about 0.5 μm to about 2μm. Average particle size refers to the d50 value of the particle sizedistribution (number average), which can be measured by the skilledartisan using known techniques for determining the particle sizedistribution.

According to embodiments, the one or more acrylamide (co)polymers areselected from water-soluble acrylamide (co)polymers. In variousembodiments, the acrylamide (co)polymers comprise at least 30% byweight, or at least 50% by weight acrylamide units with respect to thetotal amount of all monomeric units in the (co)polymer.

Optionally, the acrylamide-(co)polymers may comprise besides acrylamideat least one additional co-monomer. In embodiments, the additionalcomonomer is a water-soluble, ethylenically unsaturated, in particularmonoethylenically unsaturated, comonomer. Additional water-solublecomonomers should be miscible with water in any ratio, but it issufficient that the monomers dissolve sufficiently in an aqueous phaseto copolymerize with acrylamide. In general, the solubility of suchadditional monomers in water at room temperature should be at least 50g/L, preferably at least 150 g/L and more preferably at least 250 g/L.

Other water soluble comonomers comprise one or more hydrophilic groups.The hydrophilic groups are in particular functional groups whichcomprise atoms selected from the group of O-, N-, S- or P-atoms.Examples of such functional groups comprise carbonyl groups >C═O, ethergroups —O—, in particular polyethylene oxide groups —(CH₂—CH₂—O—)_(n)—,where n is preferably a number from 1 to 200, hydroxy groups —OH, estergroups —C(O)O—, primary, secondary or tertiary amino groups, ammoniumgroups, amide groups —C(O)—NH— or acid groups such as carboxyl groups—COOH, sulfonic acid groups —SO₃H, phosphonic acid groups —PO₃H₂ orphosphoric acid groups —PO₄H₂.

Monoethylenically unsaturated comonomers comprising acid groups includemonomers comprising —COOH groups, such as acrylic acid or methacrylicacid, crotonic acid, itaconic acid, maleic acid or fumaric acid,monomers comprising sulfonic acid groups, such as vinylsulfonic acid,allylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid,2-methacrylamido-2-methylpropanesulfonic acid,2-acrylamidobutanesulfonic acid, 3-acrylamido-3-methylbutanesulfonicacid or 2-acrylamido-2,4,4-trimethylpentanesulfonic acid, or monomerscomprising phosphonic acid groups, such as vinylphosphonic acid,allylphosphonic acid, N-(meth)acrylamidoalkylphosphonic acids or(meth)acryloyloxyalkylphosphonic acids. Of course the monomers may beused as salts.

The —COOH groups in polyacrylamide-copolymers may not only be obtainedby copolymerizing acrylamide and monomers comprising —COOH groups butalso by hydrolyzing derivatives of —COOH groups after polymerization.For example, amide groups —CO—NH₂ of acrylamide may hydrolyze thusyielding —COOH groups.

Also to be mentioned are derivatives of acrylamide thereof, such as, forexample, N-methyl(meth)acrylamide, N,N′-dimethyl(meth)acrylamide, andN-methylolacrylamide, N-vinyl derivatives such as N-vinylformamide,N-vinylacetamide, N-vinylpyrrolidone or N-vinylcaprolactam, and vinylesters, such as vinyl formate or vinyl acetate. N-vinyl derivatives maybe hydrolyzed after polymerization to vinylamine units, vinyl esters tovinyl alcohol units.

Further comonomers include monomers comprising hydroxy and/or ethergroups, such as, for example, hydroxyethyl(meth)acrylate,hydroxypropyl(meth)acrylate, allyl alcohol, hydroxyvinyl ethyl ether,hydroxyl vinyl propyl ether, hydroxyvinyl butyl ether orpolyethyleneoxide(meth)acrylates.

Other comonomers are monomers having ammonium groups, i.e monomershaving cationic groups. Examples comprise salts of 3-trimethylammoniumpropylacrylamides or 2-trimethylammonium ethyl(meth)acrylates, forexample the corresponding chlorides, such as 3-trimethylammoniumpropylacrylamide chloride (DIMAPAQUAT) and 2-trimethylammonium ethylmethacrylate chloride (MADAME-QUAT).

Yet other comonomers include monomers which may cause hydrophobicassociation of the (co)polymers. Such monomers comprise besides theethylenic group and a hydrophilic part also a hydrophobic part. Suchmonomers are disclosed, for instance, in WO 2012/069477 A1.

In certain embodiments, each of the one or more acrylamide-(co)polymersmay optionally comprise crosslinking monomers, i.e. monomers comprisingmore than one polymerizable group. In certain embodiments, the one ormore acrylamide-(co)polymers may optionally comprise crosslinkingmonomers in an amount of less than about 0.5%, or about 0.1%, by weight,based on the amount of all monomers.

In an embodiment, each of the one or more acrylamide-(co)polymerscomprises at least one monoethylenically unsaturated comonomercomprising acid groups, for example monomers which comprise at least onegroup selected from —COOH, —SO₃H, —PO₃H₂ or —PO₄H₂ Examples of suchmonomers include but are not limited to acrylic acid, methacrylic acid,vinylsulfonic acid, allylsulfonic acid or2-acrylamido-2-methylpropanesulfonic acid, particularly preferablyacrylic acid and/or 2-acrylamido-2-methylpropanesulfonic acid and mostpreferred acrylic acid or the salts thereof. The amount of suchcomonomers comprising acid groups may be from about 0.1% to about 70%,about 1% to about 50%, or about 10% to about 50% by weight based on theamount of all monomers.

In an embodiment, each of the one or more acrylamide-(co)polymerscomprise from about 50% to about 90% by weight of acrylamide units andfrom about 10% to about 50% by weight of acrylic acid units and/or theirrespective salts. In an embodiment, each of the one or moreacrylamide-(co)polymers comprise from about 60% to 80% by weight ofacrylamide units and from 20% to 40% by weight of acrylic acid units.

In embodiments, the one or more acrylamide-(co)polymers have a weightaverage molecular weight (M_(w)) of greater than about 5,000,000 Dalton,or greater than about 10,000,000 Dalton, or greater than about15,000,000 Dalton, or greater than about 20,000,000 Dalton; or greaterthan about 25,000,000 Dalton.

In embodiments, the solution viscosity (SV) of a solution of the liquidpolymer or inverse emulsion composition having 0.1% active polymer in a1.0 M NaCl aqueous solution at 25° C., is greater than about 3.0 cP, orgreater than about 5 cP, or greater than about 7 cP. The SV of theliquid polymer or inverse emulsion composition may be selected based, atleast in part, on the intended actives concentration of the invertedpolymer solution, to provide desired performance characteristics in theinverted polymer solution. For example, in embodiments, where theinverted polymer solution is intended to have an actives concentrationof about 2000 ppm, it is desirable that the SV of a 0.1% solution of theliquid polymer or inverse emulsion composition is in the range of about7.0 to about 8.6, because at this level, the inverted polymer solutionhas desired FR1.2 and viscosity properties. A liquid polymer or inverseemulsion composition with a lower or higher SV range may still providedesirable results, but may require changing the actives concentration ofthe inverted polymer solution to achieve desired FR1.2 and viscosityproperties. For example, if the liquid polymer or inverse emulsioncomposition has a lower SV range, it would be desirable to increase theactives concentration of the inverted polymer solution.

In embodiments, the amount of the one or more acrylamide-(co)polymers inthe liquid polymer composition is at least about 39% by weight based onthe total amount of all components of the composition (beforedissolution). In embodiments, the amount of the one or moreacrylamide-(co)polymers in the liquid polymer composition is from about39% to about 80%, or about 40% to about 60%, or about 45% to about 55%by weight based on the total amount of all components of the composition(before dissolution). In embodiments, the amount of the one or moreacrylamide-(co)polymers in the liquid polymer composition is about 39%,40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%,54%, 55%, 56%, 57%, 58%, 59% or about 60% or higher, by weight based onthe total amount of all components of the composition (before dilution).

In embodiments, the amount of the one or more acrylamide-(co)polymers inthe inverse emulsion composition is less than about 35% or less thanabout 30% by weight based on the total amount of all components of thecomposition (before dissolution). In embodiment, the amount of the oneor more acrylamide-(co)polymers in the inverse emulsion composition isfrom about 10% to about 35%, or about 15% to about 30%, or about 20% toabout 30% by weight based on the total amount of all components of thecomposition (before dissolution). In embodiments, the amount of the oneor more acrylamide-(co)polymers in the inverse emulsion composition isabout 35%, 34%, 33%, 32%, 31%, 30%, 29%, 28%, 27%, 26%, 25%, 24%, 23%,22%, 21%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 13%, 11%, or about 10%or lower, by weight based on the total amount of all components of thecomposition (before dilution).

Hydrophobic Liquid

In embodiments, the liquid polymer or inverse emulsion compositioncomprises a hydrophobic liquid component. Any suitable hydrophobicliquid component may be used. The hydrophobic liquid component includesat least one hydrophobic liquid.

In embodiments, the one or more hydrophobic liquids are organichydrophobic liquids. In embodiments, the one or more hydrophobic liquidseach have a boiling point at least about 100° C., about 135° C. or about180° C. If the organic liquid has a boiling range, the term “boilingpoint” refers to the lower limit of the boiling range.

In embodiments, the one or more hydrophobic liquids are aliphatichydrocarbons, aromatic hydrocarbons or mixtures thereof. hydrophobicliquids include but are not limited to: water-immiscible solvents, suchas paraffin hydrocarbons, naphthene hydrocarbons, aromatic hydrocarbons,olefins, oils, stabilizing surfactants and mixtures thereof. Theparaffin hydrocarbons may be saturated, linear, or branched paraffinhydrocarbons. Aromatic hydrocarbons include, but are not limited to,toluene and xylene. In embodiments, the hydrophobic liquids compriseoils, for example, vegetable oils, such as soybean oil, rapeseed oil andcanola oil, and any other oil produced from the seed of any of severalvarieties of the rape plant.

In embodiments, the amount of the one or more hydrophobic liquids in theliquid polymer or inverse emulsion composition is from about 20% toabout 60%, about 25% to about 55%, or about 35% to about 50% by weightbased on the total amount of all components of the liquid dispersionpolymer composition.

Emulsifying Surfactants

In embodiments, the liquid polymer or inverse emulsion compositionoptionally comprises one or more emulsifying surfactants.

In embodiments, the one or more emulsifying surfactants are surfactantscapable of stabilizing water-in-oil emulsions. Emulsifying surfactants,among other things, lower the interfacial tension between the water andthe water-immiscible liquid in the liquid polymer or inverse emulsioncomposition, so as to facilitate the formation of a water-in-oil polymeremulsion. It is known in the art to describe the capability ofsurfactants to stabilize water-in-oil-emulsions or oil-in-wateremulsions by using the so called “HLB-value” (hydrophilic-lipophilicbalance). The HLB-value usually is a number from 0 to 20. In surfactantshaving a low HLB-value, the lipophilic parts of the molecule predominateand consequently they are usually good water-in-oil emulsifiers. Insurfactants having a high HLB-value the hydrophilic parts of themolecule predominate and consequently they are usually good oil-in-wateremulsifiers. In embodiments, the one or more emulsifying surfactants aresurfactants have an HLB-value of about 2 to about 10, or the mixture ofthe one or more emulsifying surfactants has an HLB-value of about 2 toabout 10.

Emulsifying surfactants include, but are not limited to, sorbitanesters, in particular sorbitan monoesters with C12-C18-groups such assorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate,sorbitan monooleate, sorbitan esters with more than one ester group suchas sorbitan tristearate, sorbitan trioleate, ethoxylated fatty alcoholswith 1 to 4 ethyleneoxy groups, e.g. polyoxyethylene (4) dodecyletherether, polyoxyethylene (2) hexadecyl ether, or polyoxyethylene (2) oleylether.

Emulsifying surfactants include, but are not limited to, emulsifiershaving HLB values in the range of about 2 to about 10, preferably lessthan about 7. Suitable such emulsifiers include the sorbitan esters,phthalic esters, fatty acid glycerides, glycerine esters, as well as theethoxylated versions of the above and any other well-known relativelylow HLB emulsifier. Examples of such compounds include sorbitanmonooleate, the reaction product of oleic acid with isopropanolamide,hexadecyl sodium phthalate, decyl sodium phthalate, sorbitan stearate,ricinoleic acid, hydrogenated ricinoleic acid, glyceride monoester oflauric acid, glyceride monoester of stearic acid, glycerol diester ofoleic acid, glycerol triester of 12-hydroxystearic acid, glyceroltriester of ricinoleic acid, and the ethoxylated versions thereofcontaining 1 to 10 moles of ethylene oxide per mole of the basicemulsifier. Thus, any emulsifier may be utilized which will permit theformation of the initial emulsion and stabilize the emulsion during thepolymerization reaction. Examples of emulsifying surfactants alsoinclude modified polyester surfactants, anhydride substituted ethylenecopolymers, N,N-dialkanol substituted fatty amides, and tallow amineethoxylates.

In an embodiment, the liquid polymer or inverse emulsion compositioncomprises about 0% to about 8%, about 0.05% to about 5%, about 0.1% toabout 5%, or about 0.5% to about 3% by weight of the one or moreemulsifying surfactants.

These emulsifying surfactants, used alone or in mixtures, are utilizedin amounts of greater than about 0.5% or greater than about 1% of thetotal liquid polymer or inverse emulsion composition.

Inverting Surfactants

In embodiments, the liquid polymer or inverse emulsion compositionoptionally comprises one or more inverting surfactants. In embodiments,the one or more inverting surfactants are surfactants which may be usedto accelerate the formation of an inverted polymer solution (e.g., a(co)polymer solution) after mixing the liquid polymer or inverseemulsion composition with an aqueous solution.

The one or more inverting surfactants are not those which are used asemulsifying surfactants in the embodiments. Inverting surfactantsinclude, but are not limited to, ethoxylated alcohols, alcoholethoxylates, ethoxylated esters of sorbitan, ethoxylated esters of fattyacids, ethoxylated fatty acid esters, and ethoxylated esters of sorbitoland fatty acids, or any combination of the preceding. Invertingsurfactants include nonionic surfactants comprising a hydrocarbon groupand a polyalkylenoxy group of sufficient hydrophilic nature. Preferably,nonionic surfactants of the general formula R¹—O—(CH(R²)—CH₂—O)_(n)H (I)may be used, wherein R¹ is a C₈-C₂₂-hydrocarbon group, preferably analiphatic C₁₀-C₁₈-hydrocarbon group, n is a number of ≥4, preferably ≥6,and R² is H, methyl or ethyl with the proviso that at least 50% of thegroups R² are H. Examples of such surfactants include polyethoxylatesbased on C₁₀-C₁₈-alcohols such as C_(12/14)-, C_(14/18)- orC_(16/18)-fatty alcohols, C₁₃- or C_(13/15)-oxoalcohols. The HLB-valuemay be adjusted by selecting the number of ethoxy groups. Specificexamples include tridecylalcohol ethoxylates comprising from 4 to 14ethylenoxy groups, e.g. tridecyalcohol·8 EO or C_(12/14) fatty alcoholethoxylates, e.g. C_(12/14)·8 EO. Examples of inverting surfactants alsoinclude modified polyester surfactants, anhydride substituted ethylenecopolymers, N,N-dialkanol substituted fatty amides, and tallow amineethoxylates.

Further inverting surfactants comprise anionic surfactants, for examplesurfactants comprising phosphate or phosphonic acid groups.

In embodiments, the amount of the one or more inverting surfactants inthe liquid polymer or inverse emulsion composition is from about 0.5% toabout 10%, or from about 1% to about 6% by weight based on the totalamount of all components of the liquid polymer or inverse emulsioncomposition.

In certain embodiments, the one or more inverting surfactants are addedto the liquid polymer or inverse emulsion composition directly afterpreparation of the composition comprising the one or more acrylamide(co)polymers dispersed in one or more hydrophobic liquids, andoptionally the one or more emulsifying surfactants (e.g., they may beadded after polymerization and/or after dewatering); i.e. the liquidpolymer or inverse emulsion composition which is transported from thelocation of manufacture to the location of use already comprises the oneor more inverting surfactants. In another embodiment the one or moreinverting surfactants may be added to the liquid polymer or inverseemulsion composition at the location of use, e.g. at an off-shoreproduction site.

Stabilizing Agents

In embodiments, the liquid polymer or inverse emulsion compositioncomprises one or more stabilizing agents, wherein at least onestabilizing agent is selected from the group consisting ofpoly(alkyl)acrylate compounds. The stabilizing agents aim at stabilizingthe dispersion of the particles of polyacrylamide-(co)polymers in theorganic, hydrophobic phase and optionally also at stabilizing thedroplets of the aqueous monomer phase in the organic hydrophobic liquidbefore and in course of the polymerization. The term “stabilizing”means, as in the usual manner, that the stabilizing agents prevent thedispersion from aggregation and flocculation, or prevent sedimentationand/or caking of the solids or particles in the composition and/orcreation of separated oil phase. As used herein, “caking” refers to theformation of lumps or masses from the solids or particles in thecomposition. Generally, hard caking is characterized by strong, adhesiveforces between the particles, and/or the formation of a cake which isdifficult to redisperse. Soft caking may be characterized by weak,adhesive forces between the particles, and/or the formation of a cakewhich is more readily redispersed. Ideally, the solids and particles ofthe composition remain substantially evenly dispersed in the liquids ofthe composition. In certain embodiments, the stabilizing agent increasesthe stability of the liquid polymer or inverse emulsion composition suchthat the composition shows no caking, or only soft caking, after about20, about 30, about 40, about 50, about 60, about 70, about 80, about 90or about 100 days at a temperature in the range of about 30 to 50° C. Incertain embodiments, compositions which undergo soft caking arere-dispersable with gentle agitation or stirring. In certainembodiments, the compositions show no caking, or only soft caking, afterabout 20, about 30, about 40, about 50, about 60, about 70, about 80,about 90 or about 100 days at a temperature in the range of about 30 to50° C. In embodiments, less than about 10%, about 5%, or about 2% of thesolids or particles in the composition have settled into a soft cakeafter about 20, about 30, about 40, about 50, about 60, about 70, about80, about 90 or about 100 days at a temperature in the range of about 30to 50° C.

In an embodiment, the liquid polymer or inverse emulsion compositioncomprises about 0.5% to about 8%, about 1% to about 5%, about 1.5% toabout 5%, or about 1.5% to about 3.5% by weight of the one or morepoly(alkyl)acrylate compounds.

The poly(alkyl)acrylate compounds used alone or in mixtures, areutilized in amounts of about 0.5% to about 1.5%, or about 0.5% to about1.5%, by weight of the total liquid polymer or inverse emulsioncomposition.

In embodiments, the composition comprises a poly(alkyl)acrylate compoundof Formula III:

Wherein R′ is a straight or branched C₆₋₁₄ alkyl group; and

p is an integer from 2000 to 5000.

In an embodiments, the poly(alkyl)acrylate compound is, for example,poly(2-ethylhexyl)acrylate.

In embodiments, the poly(2-ethylhexyl)acrylate has a MW in the rangeabout 90000 to 95000 Daltons.

In embodiments, the compositions may further comprise additionalstabilizing agents, for example agents which aim at such stabilizationof the dispersion or emulsion, such as oligomeric or polymericsurfactants. Due to the fact that oligomeric and polymeric surfactantshave many anchor groups they absorb very strongly on the surface of theparticles and furthermore oligomers/polymers are capable of forming adense steric barrier on the surface of the particles which preventsaggregation. The number average molecular weight Mn of such oligomericor polymeric surfactants may for example range from 500 to 60,000Daltons, from 500 to 10,000 Daltons, or from 1,000 to 5,000 Daltons.Oligomeric and/or polymeric surfactants for stabilizing polymerdispersions are known to the skilled artisan. Examples of suchstabilizing polymers comprise amphiphilic copolymers, comprisinghydrophilic and hydrophobic moiety, amphiphilic copolymers comprisinghydrophobic and hydrophilic monomers and amphiphilic comb polymerscomprising a hydrophobic main chain and hydrophilic side chains oralternatively a hydrophilic main chain and hydrophobic side chains.

Examples of amphiphilic copolymers comprise copolymers comprising ahydrophobic moiety comprising alkylacrylates having longer alkyl chains,e.g. C6 to C22-alkyl chains, such as for instance hexyl(meth)acrylate,2-ethylhexyl(meth)acrylate, octyl(meth)acrylate, do-decyl(meth)acrylate,hexadecyl(meth)acrylate or octadecyl(meth)acrylate. The hydrophilicmoiety may comprise hydrophilic monomers such as acrylic acid,methacrylic acid or vinyl pyrrolidone.

In an embodiment, the liquid polymer or inverse emulsion compositioncomprises about 0% to about 8%, about 0.1% to about 5%, or about 1% toabout 5% by weight of the one or more additional stabilizing agentsdescribed herein.

Other Components

In embodiments, the liquid polymer or inverse emulsion composition mayoptionally comprise one or more additional components, for example toprovide necessary or desirable properties to the composition or to theapplication. Examples of such components comprise radical scavengers,oxygen scavengers, chelating agents, biocides, stabilizers, orsacrificial agents.

Preparation of Liquid Polymer and Inverse Emulsion Compositions

In embodiments, the liquid polymer or inverse emulsion composition maybe synthesized according to the following procedures.

In a first step, an inverse emulsion (water-in-oil emulsion) ofacrylamide-(co)polymers is synthesized using procedures known to theskilled artisan. Such inverse emulsions are obtained by polymerizing anaqueous solution of acrylamide and other comonomers, such aswater-soluble ethylenically unsaturated comonomers, emulsified in ahydrophobic oil phase. In certain embodiments, in a following step,water within such inverse emulsions is reduced to an amount of less thanabout 12%, or less than about 10%, or less than about 5%, by weight.Such techniques are described, for instance, in U.S. Pat. Nos.4,052,353, 4,528,321, or DE 24 19 764 A1.

For the polymerization, an aqueous monomer solution comprisingacrylamide and optionally other comonomers is prepared. Acrylamide is asolid at room temperature and aqueous solutions comprising around 50% byweight of acrylamide are commercially available. If comonomers withacidic groups such as acrylic acid are used the acidic groups may beneutralized by adding aqueous bases such as aqueous sodium hydroxide.The concentration of all monomers together in the aqueous solutionshould usually be about 10% to about 60% by weight based on the total ofall components of the monomer solution, or from about 30% to about 50%,or about 35% to about 45% by weight.

The aqueous solution of acrylamide and comonomers is emulsified in theone or more hydrophobic liquids using one or more emulsifyingsurfactants. The one or more emulsifying surfactants may be added to themixture or may be added before to the monomer solution or thehydrophobic liquid. Other surfactants may be used in addition to the oneor more emulsifying surfactants, such as a stabilizing surfactant.Emulsifying may be done in the usual manner, e.g. by stirring themixture.

After an emulsion has been formed polymerization may be initiated byadding an initiator which results in generation of a suitable freeradical. Any known free radical initiator may be employed. Theinitiators may be dissolved in a solvent, including but not limited towater or water miscible organic solvents, such as alcohols, and mixturesthereof. The initiators may also be added in the form of an emulsion.Initiators include, but are not limited to: azo compounds including2,2′-azobis(2-amidinopropane) dihydrochloride,2,2′-azobis[2-(2-imidazolin-2-yl)propane], 2,2′-azobis(isobutyronitrile)(AIBN), 2,2′-azobis(2,4-dimethylvaleronitrile) (AIVN),2,2′-azobis(2-methylpropionamidine) dihydrochloride, and the like. Otherinitiators include peroxide initiators, for example benzoyl peroxide,t-butyl peroxide, t-butyl hydroperoxide and t-butyl perbenzoate. Otherinitiators include, for example, sodium bromate/sulfur dioxide,potassium persulfate/sodium sulfite, and ammonium persulfate/sodiumsulfite, as well as initiators disclosed in U.S. Pat. No. 4,473,689.

In certain embodiments, one or more chain transfer agents may be addedto the mixture during polymerization. Generally, chain transfer agentshave at least one weak chemical bond, which therefore facilitates thechain transfer reaction. Any conventional chain transfer agent may beemployed, such as propylene glycol, isopropanol, 2-mercaptoethanol,sodium hypophosphite, dodecyl mercaptan, thioglycolic acid, other thiolsand halocarbons, such as carbon tetrachloride. The chain transfer agentis generally present in an amount of about 0.001 percent to about 10percent by weight of the total emulsion, though more may be used.

The polymerization temperature usually is from about 30° C. to about100° C., or about 30° C. to about 70° C., or about 35° C. to about 60°C. Heating may be done by external sources of heat and/or heat may begenerated by the polymerization reaction itself, in particular whenstarting polymerization. Polymerization times may for example be fromabout 0.5 h to about 10 h.

The polymerization yields an inverse emulsion comprising an aqueousphase of the one or more acrylamide-(co)polymers dissolved or swollen inwater wherein the aqueous phase is emulsified in an organic phasecomprising the one or more hydrophobic liquids.

In order to convert the inverse emulsion obtained to the liquid polymercompositions to be used in the methods described herein, after thepolymerization, some or all of the water is distilled off from theemulsion thus yielding particles of the one or moreacrylamide-(co)polymers dispersed in the one or more hydrophobicliquids. Liquid polymer compositions having lower water content mayprovide many of the same advantages as inverse emulsions, but withsignificantly reduced water content. They may provide a more convenient,economically viable delivery form that offers improved properties to theemulsions or dry polymers. Because of the low/no water content they aresubstantially a dispersion of the polymer in a hydrophobic oil phase.Some liquid polymers and their manufacture are disclosed, for example,in German Patent Publication No. 2419764 A1, U.S. Pat. Nos. 4,052,353,4,528,321, 6,365,656 B1, or 6,833,406 B1 (each of which is incorporatedherein by reference in its entirety).

For the liquid polymer compositions, the water is removed to a level ofless than about 12%, or less than about 10%, or less than about 7%, orless than about 5%, or less than about 3% by weight. In embodiments, theremoval of water is carried out by any suitable means, for example, atreduced pressure, e.g. at a pressure of about 0.00 to about 0.5 bars, orabout 0.05 to about 0.25 bars. The temperature for water removal stepsmay typically be from about 50° C. to about 150° C., although techniqueswhich remove water at higher temperatures may be used. In certainembodiments, one or more of the hydrophobic liquids used in the inverseemulsion may be a low boiling liquid, which can distill off togetherwith the water as a mixture.

Before or after removal of the amount of water desired, the one or moreinverting surfactants, and other optional components, may be added.

In embodiments, the one or more poly(alkyl)acrylate compounds are addedto a liquid polymer or an inverse emulsion composition comprising one ormore acrylamide-(co)polymers, one or more hydrophobic liquids, one ormore emulsifier surfactants, and one or more inverting surfactants. Incertain embodiments, the composition is agitated or stirred after theaddition of the one or more stabilizing agents as necessary to mix theone or more stabilizing agents into the composition, for example, for aperiod of at least about 20 minutes.

In embodiments, the one or more stabilizing agents may be added at anypoint during the preparation of a liquid polymer or inverse emulsioncomposition as long as it does not adversely impact the formation orresulting properties of the liquid polymer or inverse emulsioncomposition. In certain embodiments, the one or more stabilizing agentsmay be added, for example, after dewatering the composition or after thestep of removing water from the composition during its preparation. Inembodiments, the one or more stabilizing agents may be added alone orwith one or more inverting surfactants. When the one or more stabilizingagents are added with the one or more inverting surfactants, they may beadded to the composition separately or substantially simultaneously, ormixed to combine and then added to the composition as a blend.

In embodiments, the manufacture of the liquid polymer or inverseemulsion compositions is carried out in chemical production plants.

Aqueous Solutions

In embodiments, the aqueous solution may comprise produced reservoirbrine, reservoir brine, sea water, fresh water, produced water, water,saltwater (e.g. water containing one or more salts dissolved therein),brine, synthetic brine, synthetic seawater brine, or any combinationthereof.

The term “brine” or “aqueous brine” as used herein refers to sea water;naturally-occurring brine; a chloride-based, bromide-based,formate-based, or acetate-based brine containing monovalent and/orpolyvalent cations or combinations thereof. Examples of suitablechloride-based brines include without limitation sodium chloride andcalcium chloride. Further without limitation, examples of suitablebromide-based brines include sodium bromide, calcium bromide, and zincbromide. In addition, examples of formate-based brines include withoutlimitation, sodium formate, potassium formate, and cesium formate.

In certain embodiments, the aqueous solution comprises about 15,000 toabout 160,000; about 15,000 to about 100,000; about 15,000 to about50,000; about 30,000 to about 40,000; about 15,000 to about 16,000 ppmtotal dissolved solids (tds). In an embodiment, the aqueous solutioncomprises a brine having about 15,000 ppm tds.

In embodiments, the aqueous solution has a temperature of from about 1°C. to about 120° C., about 4° C. to about 45° C., or about 45° C. toabout 95° C.

Generally, the aqueous solution may comprise water from any readilyavailable source, provided that it does not contain an excess ofcompounds that can adversely affect other components in the invertedpolymer solution or render the inverted polymer solution unsuitable forits intended use (e.g., unsuitable for use in an oil and gas operationsuch as an EOR operation). If desired, the aqueous solution obtainedfrom naturally occurring sources may be treated prior to use. Forexample, the aqueous solution may be softened (e.g., to reduce theconcentration of divalent and trivalent ions in the aqueous fluid) orotherwise treated to adjust their salinity. In certain embodiments, theaqueous solution may comprise soft brine or hard brine. In certainembodiments, the aqueous solution may comprise produced reservoir brine,reservoir brine, sea water, or a combination thereof.

In one embodiment, seawater is used as aqueous solution, since off-shoreproduction facilities tend to have an abundance of seawater available,limited storage space, and transportation costs to and from an off-shoresite are typically high. If seawater is used as the aqueous solution, itmay be softened prior to the addition of the suspended polymer, therebyremoving multivalent ions in the water (e.g., specifically Mg²⁺ andCa²⁺).

Preparation of Inverted Polymer Solutions

According to various embodiments, a method for preparing an invertedpolymer solution may include inverting and diluting a liquid polymer orinverse emulsion composition according to the embodiments describedherein in an aqueous solution to provide an inverted polymer solution.In embodiments, the liquid polymer or inverse emulsion composition andan aqueous solution are mixed until the liquid polymer or inverseemulsion composition is inverted in an aqueous solution to provide aninverted polymer solution. Various processes may be employed to preparethe inverted polymer solutions. The inverted polymer solutions areuseful, for example, in methods of enhanced oil recovery or in frictionreduction applications. In embodiments, an inverted polymer solutioncomprises a liquid polymer or inverse emulsion composition according tothe embodiments and an aqueous solution. In embodiments, an invertedpolymer solution comprises a liquid polymer or inverse emulsioncomposition according to the embodiments, which has been inverted in anaqueous solution.

According to various embodiments, a method for enhanced oil recovery mayinclude inverting and/or diluting a liquid polymer or inverse emulsioncomposition according to the embodiments described herein in an aqueoussolution to provide an inverted polymer solution. In embodiments, theliquid polymer or inverse emulsion composition and an aqueous solutionare mixed until the liquid polymer composition is inverted in theaqueous solution to provide an inverted polymer solution.

In embodiments, the liquid polymer or inverse emulsion composition isinverted and diluted in the aqueous solution to provide an invertedpolymer solution having an active polymer concentration of acrylamide(co)polymer between about 50 to about 15,000 ppm, or about 500 and about5000 ppm. In embodiments, the inverted polymer solution has an FR1.2 ofabout 1.5 or less. In embodiments, the inverted polymer solution has anFR1.2 of about 1.1 to about 1.3. In embodiments, the inverted polymersolution has an FR1.2 of about 1.2 or less.

In some embodiments, the inverted polymer solution can have aconcentration of one or more synthetic (co)polymers (e.g., one or moreacrylamide (co)polymers) of at least 50 ppm (e.g., at least 100 ppm, atleast 250 ppm, at least 500 ppm, at least 750 ppm, at least 1000 ppm, atleast 1500 ppm, at least 2000 ppm, at least 2500 ppm, at least 3000 ppm,at least 3500 ppm, at least 4000 ppm, at least 4500 ppm, at least 5000ppm, at least 5500 ppm, at least 6000 ppm, at least 6500 ppm, at least7000 ppm, at least 7500 ppm, at least 8000 ppm, at least 8500 ppm, atleast 9000 ppm, at least 9500 ppm, at least 10,000 ppm, at least 10,500ppm, at least 11,000 ppm, at least 11,500 ppm, at least 12,000 ppm, atleast 12,500 ppm, at least 13,000 ppm, at least 13,500 ppm, at least14,000 ppm, or at least 14,500 ppm).

In some embodiments, the inverted polymer solution can have aconcentration of one or more synthetic (co)polymers (e.g., one or moreacrylamide (co)polymers) of 15,000 ppm or less (e.g., 14,500 ppm orless, 14,000 ppm or less, 13,500 ppm or less, 13,000 ppm or less, 12,500ppm or less, 12,000 ppm or less, 11,500 ppm or less, 11,000 ppm or less,10,500 ppm or less, 10,000 ppm or less, 9,500 ppm or less, 9,000 ppm orless, 8,500 ppm or less, 8,000 ppm or less, 7,500 ppm or less, 7,000 ppmor less, 6,500 ppm or less, 6,000 ppm or less, 5,500 ppm or less, 5,000ppm or less, 4500 ppm or less, 4000 ppm or less, 3500 ppm or less, 3000ppm or less, 2500 ppm or less, 2000 ppm or less, 1500 ppm or less, 1000ppm or less, 750 ppm or less, 500 ppm or less, 250 ppm or less, or 100ppm or less).

The inverted polymer solution can have a concentration of one or moresynthetic (co)polymers (e.g., one or more acrylamide (co)polymers)ranging from any of the minimum values described above to any of themaximum values described above. For example, in some embodiments, theinverted polymer solution can have a concentration of one or moresynthetic (co)polymers (e.g., one or more acrylamide (co)polymers) offrom 500 to 5000 ppm (e.g., from 500 to 3000 ppm, or from 500 to 1500ppm).

In some embodiments, the inverted polymer solution can be an aqueousunstable colloidal suspension. In other embodiments, the invertedpolymer solution can be an aqueous stable solution.

In some embodiments, the inverted polymer solution can have a filterratio of 1.5 or less (e.g., 1.45 or less, 1.4 or less, 1.35 or less, 1.3or less, 1.25 or less, 1.2 or less, 1.15 or less, 1.1 or less, or lessthan 1.05) at 15 psi using a 1.2 μm filter. In some embodiments, theinverted polymer solution can have a filter ratio of greater than 1(e.g., at least 1.05, at least 1.1, at least 1.15, at least 1.2, atleast 1.25, at least 1.3, at least 1.35, at least 1.4, or at least 1.45)at 15 psi using a 1.2 μm filter.

The inverted polymer solution can have a filter ratio at 15 psi using a1.2 μm filter ranging from any of the minimum values described above toany of the maximum values described above. For example, in someembodiments, the inverted polymer solution can have a filter ratio offrom 1 to 1.5 (e.g., from 1.1 to 1.4, or from 1.1 to 1.3) at 15 psiusing a 1.2 μm filter.

In certain embodiments, the inverted polymer solution can have aviscosity based on shear rate, temperature, salinity, polymerconcentration, and polymer molecular weight. In some embodiments, theinverted polymer solution can have a viscosity of from 2 cP to 100 cP,where the 2 cP to 100 cP is an output using the ranges in the followingtable:

Polymer viscosity (cP) 2~100 Shear rate (1/sec) 0.1~1000  Temperature (°C.) 1~120 Salinity (ppm)    0~250,000 Polymer concentration (ppm) 50~15,000 Polymer molecular weight (Dalton) 2M~26M 

In embodiments, the time required for the liquid polymer or inverseemulsion composition to invert in the aqueous solution once thedissolution begins is less than 30 minutes.

Methods of Use

The inverted polymer solutions described herein can be used in a varietyof oil and gas operations, including an EOR operation, an improved oilrecovery (IOR) operation, a polymer flooding operation, an AP floodingoperation, a SP flooding operation, an ASP flooding operation, aconformance control operation, a hydraulic fracturing operation, afriction reduction operation, or any combination thereof. The invertedpolymer solutions can even be used in water treatment operationsassociated with oil and gas operations. In one embodiment, the invertedpolymer solution can be used as an injection fluid. In anotherembodiment, the inverted polymer solution can be included in aninjection fluid. In another embodiment, the inverted polymer solutioncan be used as a hydraulic fracturing fluid. In another embodiment, theinverted polymer solution can be included in a hydraulic fracturingfluid. In another embodiment, the inverted polymer solution can be usedas a drag reducer that reduces friction during transportation of a fluidin a pipeline. In another embodiment, the inverted polymer solution canbe included in a drag reducer that reduces friction duringtransportation of a fluid in a pipeline. In short, in certainembodiments, the inverted polymer solutions described herein can be usedin hydrocarbon recovery.

Methods of hydrocarbon recovery can comprise providing a subsurfacereservoir containing hydrocarbons therewithin; providing a wellbore influid communication with the subsurface reservoir; preparing an invertedpolymer solution using the methods described above; and injecting theinverted polymer solution through the wellbore into the subsurfacereservoir. For example, the subsurface reservoir can be a subseareservoir and/or the subsurface reservoir can have a permeability offrom 10 millidarcy to 40,000 millidarcy.

The wellbore in the second step can be an injection wellbore associatedwith an injection well, and the method can further comprise providing aproduction well spaced-apart from the injection well a predetermineddistance and having a production wellbore in fluid communication withthe subsurface reservoir. In these embodiments, injection of theinverted polymer solution can increase the flow of hydrocarbons to theproduction wellbore.

In some embodiments, methods of hydrocarbon recovery can further includea recycling step. For example, in some embodiments, methods ofhydrocarbon recovery can further comprise producing production fluidfrom the production well, the production fluid including at least aportion of the injected inverted polymer solution; and using theproduction fluid to invert an additional liquid polymer or inverseemulsion composition, for example, to form a second inverted polymersolution. The second inverted polymer solution can be injected into atleast one wellbore (e.g., an injection well, the same wellbore discussedin the second step or a different wellbore, etc.). Thus, in someembodiments, the inverted polymer solution is included in an injectionfluid.

The wellbore in the second step can be a wellbore for hydraulicfracturing that is in fluid communication with the subsurface reservoir.Thus, in one embodiment, the inverted polymer solution injected in thefourth step functions as a drag reducer that reduces friction duringinjection in the fourth step. By doing so, the inverted polymer solutionis used as a drag reducer that reduces friction during transportation ofa fluid (e.g., the hydraulic fracturing fluid) in a pipeline (e.g., thewellbore or components thereof). In another embodiment, the invertedpolymer solution is included in a hydraulic fracturing fluid.

The liquid polymer or inverse emulsion composition and the invertedpolymer solutions according to the embodiments may be used in asubterranean treatment. Such subterranean treatments include, but arenot limited to, drilling operations, stimulation treatments, productionand completion operations. Those of ordinary skill in the art, with thebenefit of this disclosure, will be able to recognize a suitablesubterranean treatment.

The liquid polymer or inverse emulsion composition or an invertedpolymer solution of the present embodiments may have various uses, forexample in crude oil development and production from oil bearingformations that can include primary, secondary or enhanced recovery.Chemical techniques, including for example injecting surfactants(surfactant flooding) to reduce interfacial tension that prevents orinhibits oil droplets from moving through a reservoir or injectingpolymers that allow the oil present to more easily mobilize through aformation, can be used before, during or after implementing primaryand/or secondary recovery techniques. Such techniques can also be usedfor enhanced oil recovery, or to complement other enhanced oil recoverytechniques.

The liquid polymer or inverse emulsion compositions and inverted polymersolutions can be utilized in such diverse processes as flocculationaids, centrifugation aids, dewatering of mineral slurries, thin liftdewatering, emulsion breaking, sludge dewatering, raw and waste waterclarification, drainage and retention aids in the manufacture of pulpand paper, flotation aids in mining processing, color removal, andagricultural applications. Generally, the liquid polymer compositionsand inverted polymer solutions described herein can be used as processaids in a variety of solid-liquid separation processes, including butnot limited to, flocculation, dewatering, clarification and/orthickening processes or applications. As referred to herein, the term“dewatering” relates to the separation of water from solid material orsoil by a solid-liquid separation process, such as by wetclassification, centrifugation, filtration or similar processes. In somecases, dewatering processes and apparatus are used to rigidify orimprove rigidification of the dispersed particulate materials in thesuspension.

The liquid polymer or inverse emulsion compositions and inverted polymersolutions described herein can be used in a variety of dewatering,clarification and/or thickening applications. For example, the liquidpolymer or inverse emulsion compositions and inverted polymer solutionscan be used in municipal and industrial waste water treatment;clarification and settling of primary and secondary industrial andmunicipal waste; potable water clarification; in applications in whichpart or all of the dewatered solids or clarified water is returned tothe environment, such as sludge composting, land application of sludge,pelletization for fertilizer application, release or recycling ofclarified water, papermaking; food processing applications such as wastedewatering, including waste dewatering of poultry beef, pork and potato,as well as sugar decoloring, sugar processing clarification, and sugarbeet clarification; mining and mineral applications, including treatmentof various mineral slurries, coal refuse dewatering and thickening,tailings thickening, and Bayer process applications such as red mudsettling, red mud washing, Bayer process filtration, hydrateflocculation, and precipitation; biotechnological applications includingdewatering and clarification of wastes, such as dewatering andclarification of fermentation broths; and the like.

In embodiments, the liquid polymer or inverse emulsion composition orinverted polymer solution may be used to dewater suspended solids. Inembodiments, a method of dewatering a suspension of dispersed solidscomprises: (a) intermixing an effective amount of the liquid polymer orinverse emulsion composition or inverted polymer solution, with asuspension of dispersed solids, and (b) dewatering the suspension ofdispersed solids.

In embodiments, a method of dewatering an aqueous suspension ofdispersed solids comprises: (a) adding an effective amount of a liquidpolymer or inverse emulsion composition or inverted polymer solution tothe suspension; (b) mixing the liquid polymer or inverse emulsioncomposition or inverted polymer solution into the suspension to form atreated suspension; and (c) subjecting the treated suspension todewatering.

The liquid polymer or inverse emulsion compositions or inverted polymersolutions may be employed in the above applications alone, inconjunction with, or serially with, other known treatments.

In embodiments, the liquid polymer or inverse emulsion compositions orinverted polymer solutions may be used in method of deinking of papermill process water.

In other embodiments, a method of clarifying industrial waste watercomprises: adding to the waste water an effective amount of a liquidpolymer or inverse emulsion composition; and clarifying the industrialwaste water.

In methods the liquid polymer or inverse emulsion compositions orinverted polymer solutions may be used as the sole treatment agent orprocess aid. In other embodiments, the liquid polymer or inverseemulsion compositions or inverted polymer solutions can be used incombination with other treatment agents and process aids. Inembodiments, the method further comprises adding an organic or inorganiccoagulant to the waste water.

In embodiments, the liquid polymer or inverse emulsion compositions orinverted polymer solutions may be used in method of sludge dewatering.

In embodiments, the liquid polymer or inverse emulsion compositions orinverted polymer solutions may be used in method of clarification ofoily waste water.

The liquid polymer or inverse emulsion compositions or inverted polymersolutions can be used to treat, clarify or demulsify such waste water.

The liquid polymer or inverse emulsion compositions or inverted polymersolutions also may be used in a method of clarifying food processingwaste.

In another embodiment, the liquid polymer or inverse emulsioncomposition or inverted polymer solution may be used in a process formaking paper or paperboard from a cellulosic stock.

Other applications which may benefit from the liquid polymer or inverseemulsion compositions or inverted polymer solutions include soilamendment, reforestation, erosion control, seed protection/growth, etc.,in which the liquid polymer composition or inverse emulsion or invertedpolymer solution is applied to soil.

The following examples are presented for illustrative purposes only, andare not intended to be limiting.

Example 1 Preparation of an Inverse Emulsion Composition

To a 1000 mL beaker (containing a magnetic stir bar), acrylamide (as a53 wt % solution in water, 276.89 g of solution) was added. The solutionwas stirred and to this was added glacial acrylic acid (63.76 g),Diethylenetriaminepentaacetic acid (Versenex 80, 40%, 0.53 g) and water(183.31 g). Sodium hydroxide (50 wt %, 70.79 g) was added slowlymaintaining the solution temperature below 30° C. until a pH of 6.0-6.5was achieved. The pH was rechecked and adjusted to 6.0-6.5, if required.

To a 1000 mL beaker (containing a magnetic stir bar) a high boilingparaffin solvent package (211.1 g) was added. The emulsifying surfactant(12.18 g) was added and the mixture was allowed to stir until thesurfactants were dissolved. The monomer solution was added to the oilphase (over a period of 30 seconds) with vigorous mixing to form thecrude monomer emulsion. Once added, the mixture was allowed to stir for20 minutes.

The crude monomer emulsion was then homogenized for 20 seconds (using aRoss ME100L homogenizer operating at 4500 rpm). The homogenized emulsionwas then transferred to a 1000 mL jacketed reactor equipped with anoverhead stirrer, nitrogen and sulfur dioxide gas inlets, thermocouple,vent, and controlled temperature recirculating bath. The reactorcontents were then sparged 1.0 hour.

The polymerization reaction was initiated, and the reaction temperaturewas maintained between about 40 and about 45° C. After the exotherm hadceased, the reaction mixture was warmed to 50° C. and held for 1.5hours. At the end of 1.5 hours, a sodium metabisulfite solution (37.5 wt%, 17.88 g) was added and allowed to mix for 10 minutes.

Example 2 Preparation of a Liquid Polymer Composition

Emulsion Preparation:

To a 1000 mL beaker (containing a magnetic stir bar), acrylamide (as a53 wt % solution in water, 276.89 g of solution was added. The solutionwas stirred and to this was added glacial acrylic acid (63.76 g),Diethylenetriaminepentaacetic acid (Versenex 80, 40%, 0.53 g) and water(183.31 g). Sodium hydroxide (50 wt %, 70.79 g) was added slowlymaintaining the solution temperature below 30° C. until a pH of 6.0-6.5was achieved. The pH was rechecked and adjusted to 6.0-6.5, if required.

To a 1000 mL beaker (containing a magnetic stir bar), a high boilingparaffin solvent package (211.1 g) was added. The emulsifying surfactant(12.18 g) was added and the mixture was allowed to stir until thesurfactants were dissolved. The monomer solution was added to the oilphase (over a period of 30 seconds) with vigorous mixing to form thecrude monomer emulsion. Once added, the mixture was allowed to stir for20 minutes.

The crude monomer emulsion was then homogenized for 20 seconds (using aRoss ME100L homogenizer operating at 4500 rpm). The homogenized emulsionwas then transferred to a 1000 mL jacketed reactor equipped with anoverhead stirrer, nitrogen and sulfur dioxide gas inlets, thermocouple,vent and controlled temperature recirculating bath. The reactor contentswere then sparged 1.0 hour.

The polymerization reaction was initiated, and the reaction temperaturemaintained between about 40° C. and about 45° C. After the exotherm hadceased, the reaction mixture was warmed to 50° C. and held for 1.5hours. At the end of 1.5 hours, a sodium metabisulfite solution (37.5 wt%, 17.88 g) was added and allowed to mix for 10 minutes.

Water Removal:

Starting emulsions were heated under vacuum in a rotary evaporator to50° C. until no further distillate condensed. Inverting surfactants werestirred into the resulting dewatered emulsions followed by dissolvingthese into stirred brine solutions.

Example 3. Preparation and Bench Storage Tests of Exemplary LiquidPolymer Compositions Comprising a Poly(Alkyl)Acrylate Stabilizing Agent

Approximately 160 g of a liquid polymer composition prepared accordingto Example 2 is combined with 6% by weight of a breaker in a 200 mLbeaker and stirred with a Teflon overhead stirrer at 500 rpm. 1% byweight of a stabilizing agent was slowly added to the composition.Stirring was maintained for at least 20 minutes before commencing thebench storage tests. The stabilizing agent included in the compositionstested was a ˜41% microemulsion of poly(2-ethylhexyl)acrylate.

Bench storage tests were carried out by placing a standard amount (forexample, 40-45 g) of the exemplary liquid polymer compositionscomprising a poly(alkyl)acrylate stabilizing agent or a control liquidpolymer composition in sample vials. The samples were kept at about 35°C. and checked for surface bleeding and caking. The samples containing1% by weight poly(alkyl)acrylate stabilizing agent did not exhibit hardcaking through 30 days.

Example 4 Preparation of Inverted Polymer Solutions from ExemplaryCompositions

A synthetic brine was prepared that included the following: Na⁺, Ca²⁺,Mg²⁺, Cl⁻, and tds of about 15,000 ppm. The brine formulation wasprepared and filtered through 0.45 μm filter before use.

Utilizing a 1000 mL beaker, Teflon coated mixing blade and an overheadstirrer, 360 g of brine was added to the beaker. The brine was agitatedat 500 rpm and the liquid polymer composition prepared in Example 2 wasadded to the brine solution through a syringe at a dosage to result in10,000 ppm, based on active polymer concentration. This was allowed tomix for 2 hours at a constant 500 rpm. This mother solution was dilutedto 2,000 ppm utilizing 80 g of the mother solution and 320 g ofadditional brine. Brine was added to the beaker first which has a mixingblade stirring with an overhead mixer at 500 rpm and the mother solutionwas added to the shoulder of the vortex in the mixing brine. This wasmixed for an additional 2 hours.

Example 5 Testing of Inverted Polymer Solutions from ExemplaryComposition for Impact on Filter Ratio

Samples of liquid polymer compositions were prepared as describedherein. Each liquid polymer composition included a standard invertingsurfactant (6% by weight). The stabilizing agent included in thecompositions tested was a ˜41% microemulsion ofpoly(2-ethylhexyl)acrylate.

Standard viscosity (SV) was measured by preparing from the liquidpolymer composition (or base emulsion) a 0.20 wt % active polymersolution in deionized water. The polymer composition was added to thewater while stirring at 500 rpm. Mixing was continued for 45 min. The0.20 wt % active polymer solution was diluted to a 0.10 wt % activepolymer solution with a 11.7 wt % NaCl solution and mixed for 15 min.The pH was adjusted to 8.0-8.5, and then filtered through 200 μm nylonmesh screen. The viscosity was measured at 25° C. on a Brookfield DV-IIIviscometer.

The liquid polymer compositions were inverted in brine as described inExample 4.

Viscosities of the brine solutions were measured utilizing an Anton PaarMC302 performing a shear rate sweep from 0.1 sec⁻¹ to 100 sec⁻¹ at acontrolled temperature of 40° C. utilizing a concentric circle spindleattachment. Data were recorded at 10 sec⁻¹ with a target viscosity of 20cP+/−1 cP.

Filter Ratio:

Filter ratio was measured two ways. The FR5 (filter ratio using a 5micron filter) was determined by passing 500 mL samples of invertedpolymer solution prepared as described above through 5 μm, 47 mmdiameter polycarbonate filter under 1 bar pressure of N₂ or argon. TheFR5 was calculated as

$\frac{{{time}\mspace{14mu} {at}\mspace{14mu} 500\mspace{14mu} g} - {{time}\mspace{14mu} {at}\mspace{14mu} 400\mspace{14mu} g}}{{{time}\mspace{14mu} {at}\mspace{14mu} 200\mspace{14mu} g} - {{tim}\; e\mspace{14mu} {at}\mspace{14mu} {100}\mspace{14mu} g}}.$

For this example, a passing result was considered FR5≤1.2. In sampleshaving an FR5>1.2 the product was considered not passing and furthertesting was not completed.

The FR1.2 (filter ratio using a 1.2 micron filter) was determined bypassing 200 mL samples of inverted polymer solution prepared asdescribed above through 1.2 μm, 47 mm diameter polycarbonate filterunder 1 bar pressure of N₂ or Argon. The FR1.2 was calculated as

$\frac{{{time}\mspace{14mu} {at}\mspace{14mu} 200\mspace{14mu} g} - {{time}\mspace{14mu} {at}\mspace{14mu} 180\mspace{14mu} g}}{{{time}\mspace{14mu} {at}\mspace{14mu} 80\mspace{14mu} g} - {{time}\mspace{14mu} {at}\mspace{14mu} 60\mspace{14mu} g}}$

and reported. For this example, a passing result was consideredFR1.2≤1.5, but the target for the examples was FR1.2<1.2.

The results of FR1.2 are shown in Table 2.

TABLE 2 Liquid Viscosity at Polymer Stabilizing 10 sec⁻¹, Filter RatioTime at sample Agent 40° C. (cP) at 1.2 μm 200 g (min) 1 none (control)18.6 1.055 10.94 1 1% by weight 19.3 1.139 12.54 2 none (control) 21.01.089 14.51 2 2% by weight 21.8 1.350 19.58

It was noted that the exemplary stabilizing agents have minimal orsubstantially no adverse effect on the filter ratio. In particular,compositions which included the exemplary stabilizing agents retainedthe property of, when the composition is inverted in an aqueoussolution, providing an inverted polymer solution having a filter ratiousing a 1.2 micron filter (FR1.2) of about 1.3, or about 1.2, or less.The poly(alkyl)acrylate stabilizing agent performs well with respect toviscosity and filter ratio when less than 2 weight % dosage is added tothe exemplary compositions.

In the preceding specification, various embodiments have been described.It will, however, be evident that various modifications and changes maybe made thereto, and additional embodiments may be implemented, withoutdeparting from the broader scope of the embodiments as set forth in theclaims that follow. The specification is accordingly to be regarded inan illustrative rather than restrictive sense.

1. A liquid polymer or inverse emulsion composition comprising: a. oneor more hydrophobic liquids having a boiling point at least about 100°C.; b. one or more acrylamide-(co)polymers; c. one or more emulsifiersurfactants; d. one or more inverting surfactants; and e. one or morepoly(alkyl)acrylate compounds; wherein, when the composition is invertedin an aqueous solution, it provides an inverted polymer solution havinga filter ratio using a 1.2 micron filter (FR1.2) of about 1.5 or less.2. The composition of claim 1, wherein the composition is a liquidpolymer composition comprising at least about 39% by weight of one ormore acrylamide-(co)polymers.
 3. The composition of claim 1, wherein thecomposition is an inverse emulsion composition comprising less thanabout 35% by weight of one or more acrylamide-(co)polymers.
 4. Thecomposition of claim 1, wherein the aqueous solution comprises producedwater, fresh water, salt water, brine, sea water or a combinationthereof.
 5. The composition of claim 1, wherein the liquid polymercomposition further comprises water in an amount of less than about 10%,by weight based on the total amount of all components of thecomposition.
 6. The composition of claim 1, wherein when the compositionis inverted in an aqueous solution to provide an inverted polymersolution comprising about 2000 ppm active polymer, the inverted polymersolution has a viscosity of at least 10 cP at 40° C.
 7. The compositionof claim 1, wherein when the composition is inverted in an aqueoussolution, the inverted polymer solution has a FR1.2 of about 1.1 toabout 1.3.
 8. The composition of claim 1, wherein when the compositionis inverted in an aqueous solution, the inverted polymer solution has aFR1.2 of about 1.2 or less.
 9. The composition of claim 1, wherein theone or more hydrophobic liquids having a boiling point at least about100° C. is selected from the group consisting of paraffin hydrocarbons,naphthene hydrocarbons, aromatic hydrocarbons, olefins, oils,stabilizing surfactants, and mixtures or combinations of the foregoing.10. The composition of claim 1, wherein each of the one or moreacrylamide-(co)polymers comprises at least 30% by weight of acrylamidemonomer units with respect to the total amount of all monomeric units inthe (co)polymer and that each of the one or more acrylamide-(co)polymerscomprises at least one additional ethylenically unsaturated monomer. 11.The composition of claim 1, wherein at least one of the one or moreacrylamide-(co)polymers comprises 2-acrylamido-2-methylpropanesulfonicacid or salts thereof.
 12. The composition of claim 1, wherein thecomposition provides the inverted polymer solution in less than 30minutes.